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Fail to serialize/deserialize immutable collections #689
Description
We have run into an issue in 5.0.0-RC4.0.0 where we serialize an immutable list and see this exception when deserializing:
Caused by: java.lang.UnsupportedOperationException: null
at java.base/java.util.Collections$UnmodifiableCollection.add(Collections.java:1058)
at com.esotericsoftware.kryo.serializers.CollectionSerializer.read(CollectionSerializer.java:235)
at com.esotericsoftware.kryo.serializers.CollectionSerializer.read(CollectionSerializer.java:43)
at com.esotericsoftware.kryo.Kryo.readObject(Kryo.java:718)
at com.esotericsoftware.kryo.serializers.ReflectField.read(ReflectField.java:114)
... 23 common frames omitted
and also
com.esotericsoftware.kryo.KryoException: Class cannot be created (missing no-arg constructor): java.util.Collections$UnmodifiableRandomAccessList
at com.esotericsoftware.kryo.util.DefaultInstantiatorStrategy.newInstantiatorOf(DefaultInstantiatorStrategy.java:111)
at com.esotericsoftware.kryo.Kryo.newInstantiator(Kryo.java:1105)
at com.esotericsoftware.kryo.Kryo.newInstance(Kryo.java:1114)
at com.esotericsoftware.kryo.serializers.CollectionSerializer.create(CollectionSerializer.java:172)
at com.esotericsoftware.kryo.serializers.CollectionSerializer.read(CollectionSerializer.java:210)
at com.esotericsoftware.kryo.serializers.CollectionSerializer.read(CollectionSerializer.java:43)
at com.esotericsoftware.kryo.Kryo.readClassAndObject(Kryo.java:799)
Here is a test to replicate one of the scenarios:
@Test(expected = KryoException.class)
public void shouldNotExplodeWhenSerializeDeserializeImmutableCollection() {
List<String> before = List.of("one", "two");
Kryo kryo = new Kryo();
kryo.setRegistrationRequired(false);
Output output = new Output(4096, 4096);
kryo.writeClassAndObject(output, before);
output.close();
kryo.readClassAndObject(new Input(output.toBytes()));
}
Activity
isaki commentedon Aug 28, 2019
You need to write your own serializer for Collections.unmodifiable*. There is no built in Kryo support for this.
MrTetrixx commentedon Aug 30, 2019
Ok, thanks!
Note that Collections.unmodifiable* has been in java since java 5 and Immutable is used more and more since it was introduced in java 9. Might be worth adding as a default feature in Kryo.
isaki commentedon Aug 30, 2019
The difficulty is that unmodifiable* are decorators. I've written my own using a bit of reflection, but I understand the risk involved and I have very targeted use cases. Also, these are not actually immutable; they just provide views that can't be modified. The owner of the decorated collection can still modify it. For true immutability, I use Guava's Immutable collections. There is also Kryo support via an add-on library for these:
https://github.com/magro/kryo-serializers
EDIT: That package has support for unmodifiable*.